The present invention relates to an illumination light source provided with light-emitting diodes.
A light-emitting diode (referred to below as xe2x80x9cLEDxe2x80x9d) is a semiconductor device that can produce an emission with a brilliant color and high efficiency in spite of its small size. The emission produced by an LED has a high color purity because of its narrow spectral half-width. Recently, blue LEDs have been put to practical use, so that LEDs are now available in the three colors red, green and blue, which makes it possible to produce white light with the LEDs.
In the prior art, LEDs have been mainly applied to display devices. For that reason, the use of LEDs as a light source for illumination purposes has not yet been researched and developed sufficiently. When LEDs are used for a display device, just the light emitted spontaneously from the LEDs should have its properties optimized. However, where LEDs are used in combination as the light source for illumination purposes, the white light, with which an object will be illuminated, should have its color rendering performance adjusted as well. In the current state of the art, LED illumination light sources with optimized color rendering performance have not yet been developed.
LEDs have excellent monochromaticity. Accordingly, if white light produced by LEDs is to be used as illumination light, this high color purity and the material characteristics that are unique to LEDs may cause various problems regarding, for example, the problem which distribution spectra to include in the LED light sources in order to obtain white light that is suitable for illumination, or the problem which luminescent materials to use for the LEDs, since the emission spectrum and the luminous efficacy may vary depending on the luminescent material of the LED.
Therefore, with the foregoing in mind, it is a main object of the present invention to provide an LED illumination light source having high efficiency and high color rendering performance.
An illumination light source according to the present invention includes four types of light-emitting diodes, wherein the four types of light-emitting diodes are a blue light-emitting diode emitting blue light, a blue-green light-emitting diode emitting blue-green light, an orange light-emitting diode emitting orange light and a red light-emitting diode emitting red light.
In an embodiment, the blue light-emitting diode has an emission wavelength peak at 420 to 470 nm, the blue-green light-emitting diode has an emission wavelength peak at 500 to 550 nm, the orange light-emitting diode has an emission wavelength peak at 570 to 600 nm, and the red light-emitting diode has an emission wavelength peak at 610 to 660 nm.
In a preferred embodiment, the blue light-emitting diode has an emission wavelength peak at 450 to 470 nm, the blue-green light-emitting diode has an emission wavelength peak at 510 to 540 nm, the orange light-emitting diode has an emission wavelength peak at 580 to 600 nm, and the red light-emitting diode has an emission wavelength peak at 625 to 650 nm.
In another embodiment, the emission wavelength peaks of the four types of light-emitting diodes are different from corresponding hypothetical emission wavelength peaks that are calculated based on results of a theoretical simulation.
It is preferable that the illumination light source has a general color rendering index of at least 90.
It is preferable that when the illumination light source has a correlated color temperature of less than 5000 K and when a color rendering performance of the illumination light source is evaluated using a blackbody source as a standard source, the illumination light source has a spectral distribution in which the luminous intensities of the blue light-emitting diode, the blue-green light-emitting diode, the orange light-emitting diode and the red light-emitting diode increase in this order.
It is preferable that when the illumination light source has a correlated color temperature of at least 5000 K and when the color rendering performance of the illumination light source is evaluated using an artificial daylight source as the standard source, the illumination light source has a spectral distribution, in which the luminous intensity of the blue light-emitting diode is higher than the luminous intensity of the blue-green light-emitting diode, and the luminous intensity of the red light-emitting diode is higher than the luminous intensity of the orange light-emitting diode.
It is preferable that a gamut area obtained by connecting four chromaticity coordinates of special color rendering indices R9 through R12 of respective test colors rendered by the illumination light source is larger than the gamut area obtained by connecting the four chromaticity coordinates of the respective test colors rendered by the standard source.
It is preferable that a ratio (Ga4) of a gamut area obtained by connecting four chromaticity coordinates of special color rendering indices R9 through R12 of the respective test colors rendered by the illumination light source to a gamut area obtained by connecting the four chromaticity coordinates of the respective test colors rendered by the standard source is larger than a ratio (Ga) of a gamut area obtained by connecting eight chromaticity coordinates of color rendering indices R1 through R8 of respective test colors rendered by the illumination light source to a gamut area obtained by connecting the eight chromaticity coordinates of the respective test colors rendered by the standard source.
It is preferable that the illumination light source has a general color rendering index of at least 90.
In an embodiment, the illumination light source further includes a phosphor that emits light when excited by emission of the light-emitting diodes.
It is preferable that the phosphor is a yellow or a green emitting phosphor that is excited by an emission of the blue light-emitting diode and emits light in a range between green and yellow, and the phosphor has an emission distribution in which a spectral half-width of the phosphor is wider than the spectral half-widths of the light-emitting diodes.
In an embodiment, the illumination light source further includes a luminous intensity control means for adjusting a luminous intensity ratio of each of the four types of light-emitting diodes.
It is preferable that an emitting site of the blue light-emitting diode and an emitting site of the orange light-emitting diode are provided within a single chip, and an emitting site of the red light-emitting diode and an emitting site of the blue-green light-emitting diode are provided within a single chip.
In an embodiment, the illumination light source includes a power supply for supplying power to the four types of LEDs. Moreover, it is preferable that a heat-dissipating part for dissipating heat from the LEDs is integrated into the illumination light source. Furthermore, it is preferable that the illumination light source further includes a reflector for reflecting light produced by the light-emitting diodes.
The illumination light source according to the present invention includes four types of light-emitting diodes, namely a blue light-emitting diode emitting blue light, a blue green light-emitting diode emitting blue-green light, an orange light-emitting diode emitting orange light, and a red light-emitting diode emitting red light. Thus, an LED illumination light source having high efficiency and high color rendering performance can be provided, using a minimum number of color LEDs as structural elements.